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1934 is the hottest year on record

The skeptic argument...

In August 2007, Steve McIntyre, who operates the site climateaudit.org, noticed a strange discontinuity in US temperature data, occurring around January 2000. McKintyre notified NASA who acknowledged the problem as an "oversight" that would be fixed in the next data refresh. The warmest year on US record is now 1934. 1998 (long trumpeted by the media as record-breaking) moves to second place (source: Daily Tech, Climate Audit).

What the science says...

Steve McIntyre's discovery of a glitch in the GISS temperature data is an impressive achievement. Make no mistake, it's an embarrassing error on the part of NASA. But what is the significance?

NASA's "Y2K" glitch

Contrary to many reports, the error wasn't a Y2K bug but a mixup over data corrections with the NOAA. NASA GISS obtain much of their temperature data from the NOAA who adjust the data to filter out primarily time-of-observation bias (although their corrections also include inhomogeneities and urban warming - more on NOAA adjustments). From January 2000, NASA were mistakenly using unadjusted data.

USA temperature versus global temperature trends

What is often overlooked is the temperature adjustments only applied to temperatures in 48 U.S. states. As the USA comprises only 2% of the globe, this has had infinitesimal effect on global trends.

The graph below (courtesy of Open Mind) compares the global temperature trend from before and after adjustments. Before the error was discovered, the trend was 0.185°C/decade. After corrections were made, the trend was still 0.185°C/decade. The change to the global mean was less than one thousandth of a degree.

from1975.jpg

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Comments

  1. The graph cannot be right. 1934 is the hottest year, with 1998 second. The graph shows 2005 as hotter than 1998. The whole thing does not ring true, it looks manufactured to promote the alarmists assertions and to minimise the exposed errors.
    [ Response: The graph is of global temperature. '1934 is the hottest year' applies to US temperature. ]
  2. Also the graph here only goes back to the end of a 30 year cooling period. And establishes this as the zero point.
    [ Response: The point of the graph is to show the miniscule difference before and after the "Y2K correction". The reason it only showed the last 30 years was because if you display an even longer period, the difference is even harder to detect. Here is the same data going back to 1880 (again courtesy of Tamino):

    befaft.jpg

    The difference between the temperature record before the Y2K correction (red dots) and after the correction (black diamonds) is insignificant anytime before 2000 and still barely noticeable after 2000. The change has had practically no detectable impact on the global warming trend over the past 30 years. As for the zero point, temperature anomaly graphs take an average over a specified period (eg - 1960 to 1990) - the temperature anomaly is the difference from this average. The period selected is arbitrary (GISS and CRU use different time periods) as the trend will be the same regardless. ]
  3. Will Nitschke (www.capitaloffice.com.au) at 21:06 PM on 20 December, 2007
    The United States shows no warming trend but that doesn't matter because it's only 2% of the surface area of the Earth, correct?

    While this is true, the concern here is that the US surface temperature records are regarded as the best in the world. If they show no warming trend, how reliable are the records of countries such as China where there has been massive urbanisation (thus increased heat from cities)? This is an open question. And a legitimate one.

    It should also be pointed out that the land surface records we have don't show warming trends in South America or Africa or Antarctica.

    I suppose the only thing we can get out of this is to consider that global warming is perhaps more regional and local in nature and impact than the term would have us assume. Or perhaps we should focus on other temperature measures as the land surface record may not be particularly accurate in and of itself.
  4. Will Nitschke (www.capitaloffice.com.au) at 00:15 AM on 21 December, 2007
    A further observation: The seasonal Arctic ice melt is significant (based at least on the short observational records that we have) and it's been argued that it is strong evidence in support of global warming. Yet this area covers only 3% of the planet.

    Could you please clarify why the 2% land mass of the United States has only an 'infinitesimal effect on global trends' yet the 3% land area of the Arctic is apparently significant 'concrete' proof? Wouldn't the way such information is selectively used or ignored, indicative of certain biases?
  5. "The United States shows no warming trend but that doesn't matter because it's only 2% of the surface area of the Earth, correct?"
    No. The U.S. definitely shows a warming trend. Look at the actual NASA correction:
    http://www.columbia.edu/~jeh1/distro_LightUpstairs_70810.pdf
    2000 is the hottest year in this graph. Also, although there is a bump in the 30's, the overall trend is clearly up.

    All that aside, global statistics are clearly what matter for a global phenomenon.

    If you look around a bit on this site you'll find plenty of references to well-averaged, peer-reviewed data (permafrost, deep ocean temps, etc.) from all over the globe showing warming that matches anthropogenic forcing.
  6. Will Nitschke - "... the US surface temperature records are regarded as the best in the world."

    Sheesh, some of you Americans have such a superiority complex! Many other nations have excellent temperature records. For example Australia. You can check out our climate statistics at the Australian Bureau of Meteorology. The temperature and rainfall trends down here are ugly and getting worse all the time.

    Besides that, the temperature of the World's oceans is monitored by a multinational project called Argo. They do it with 3000 floats that alternately rise and sink through the top 2km of as they drift around the oceans.

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